The present invention relates to recombinant DNA technology, and in particular to introducing and expressing foreign genes in a eukaryotic cell.
The Alphavirus genus includes a variety of viruses all of which are members of the Togaviridae family. The alphaviruses include Eastern Equine Encephalitis virus (EEE), Venezuelan Equine Encephalitis virus (VEE), Everglades virus, Mucambo virus, Pixuna virus, Western Equine Encephalitis virus (WEE), Sindbis virus, Semliki Forest virus, Middelburg virus, Chikungunya virus, O""nyong-nyong virus, Ross River virus, Barmah Forest virus, Getah virus, Sagiyama virus, Bebaru virus, Mayaro virus, Una virus, Aura virus, Whataroa virus, Babanki virus, Kyzylagach virus, Highlands J virus, Fort Morgan virus, Ndumu virus, and Buggy Creek virus. The viral genome is a single-stranded, messenger-sense RNA, modified at the 5xe2x80x2-end with a methylated cap, and at the 3xe2x80x2-end with a variable-length poly (A) tract. Structural subunits containing a single viral protein, C, associate with the RNA genome in an icosahedral nucleocapsid. In the virion, the capsid is surrounded by a lipid envelope covered with a regular array of transmembranal protein spikes, each of which consists of a heterodimeric complex of two glycoproteins, E1 and E2. See Pedersen et al., J. Virol. 14:40 (1974). The Sindbis and Semliki Forest viruses are considered the prototypical alphaviruses, and have been studied extensively. See Schlesinger, The Togaviridae and Flaviviridae, Plenum Publishing Corp., New York (1986). The VEE virus has been studied by the present inventors. See U.S. Pat. No. 5,185,440 to Davis et al.
The study of these viruses has led to the development of beneficial techniques for vaccinating against the alphavirus diseases, and other diseases through the use of alphavirus vectors for the introduction of foreign DNA. See U.S. Pat. No. 5,185,440 to Davis et al., and PCT Publication WO 92/10578. The introduction of foreign DNA into eukaryotic cells has become a topic of increasing interest. It is well known that live, attenuated viral vaccines are among the most successful means of controlling viral disease. However, for some virus pathogens, immunization with a live virus strain may be either impractical or unsafe. One alternative strategy is the insertion of sequences encoding immunizing antigens of such agents into a vaccine strain of another virus. One such system utilizing a live VEE vector is described in U.S. Pat. No. 5,505,947 to Johnston et al. Another such system is described by Hahn et al., Proc. Natl. Acad. Sci. USA 89:2679 (1992), wherein Sindbis virus constructs which express a truncated form of the influenza hemagglutinin protein are described. Unfortunately, relatively few such systems are currently available.
Accordingly, there remains a need in the art for nucleic acid sequences encoding foreign antigens to be safely incorporated into a vaccine strain of a virus, which may be then be utilized as a vaccine for the foreign antigen.
As a first aspect, the present invention provides a helper cell for expressing an infectious, replication defective, alphavirus particle in an alphavirus-permissive cell. The helper cell includes (a) a first helper RNA encoding (i) at least one alphavirus structural protein, and (ii) not encoding at least one alphavirus structural protein; and (b) a second helper RNA separate from the first helper RNA, the second helper RNA (i) not encoding the at least one alphavirus structural protein encoded by the first helper RNA, and (ii) encoding at least one alphavirus structural protein not encoded by the first helper RNA, such that the alphavirus structural proteins assemble together into alphavirus particles in the cell. Preferably, the alphavirus packaging segment is deleted from at least the first helper RNA, and is more preferably deleted from both the first helper RNA and second helper RNA.
In a preferred embodiment, the helper cell is co-transfected with a replicon RNA, which encodes the alphavirus packaging segment and an inserted heterologous RNA. In the embodiment wherein the helper cell also includes a replicon RNA, the alphavirus packaging segment may be, and preferably is, deleted from both the first helper RNA and the second helper RNA. For example, in the embodiment wherein the helper cell includes a replicon RNA encoding the alphavirus packaging segment and an inserted heterologous RNA, the first helper RNA encodes the alphavirus E1 glycoprotein and the alphavirus E2 glycoprotein, and the second helper RNA encodes the alphavirus capsid protein. The replicon RNA, first helper RNA, and second helper RNA are all on separate molecules and are co-transfected into the host cell.
In an alternative embodiment, the helper cell includes a first helper RNA encoding the alphavirus E1 glycoprotein and the alphavirus E2 glycoprotein, and is co-transfected with a replicon RNA encoding the alphavirus packaging segment, an inserted heterologous RNA, and the remaining alphavirus structural proteins not encoded by a first helper RNA. Thus, the replicon RNA and the first helper RNA are on separate molecules, and the replicon RNA and the RNA encoding a structural protein not encoded by the first helper RNA are on a single molecule. The heterologous RNA comprises a foreign RNA which encodes for proteins or peptides which are desirably expressed in the helper cell.
The RNA encoding the structural proteins, i.e., the first helper RNA and the second helper RNA, may advantageously include one or more attenuating mutations. In the preferred embodiment, at least one of the first helper RNA and the second helper RNA includes at least one attenuating mutation. The attenuating mutations provide the advantage that in the event of RNA recombination within the cell, the conjoining of the structural and non-structural genes will produce a virus of decreased virulence.
As a second aspect, the present invention provides a method of making infectious, replication defective, alphavirus particles. The method includes co-transfecting a helper cell as given above with a replicon RNA, producing the alphavirus particles in the transfected cell, and then collecting the alphavirus particles from the cell. The replicon RNA encodes the alphavirus packaging segment, non-structural proteins and a heterologous RNA. The non-structural proteins encoded by the replicon RNA may be such proteins as are required for replication and transcription. The transfected cell further includes the first helper RNA and second helper RNA as described above.
As a third aspect, the present invention provides a set of RNAs for expressing an infectious, replication defective alphavirus. The set of RNAs comprises, in combination, (a) a replicon RNA encoding a promoter sequence, an inserted heterologous RNA, wherein RNA encoding at least one structural protein of the alphavirus is deleted from the replicon RNA, and (b) a first helper RNA separate from the replicon RNA, wherein the first helper RNA encodes in trans, the structural protein which is deleted from the replicon RNA, and a promoter sequence. In this embodiment, it is preferred that an RNA segment encoding at least one of the structural proteins is located on an RNA other than the first helper RNA. Thus, for example, the set of RNAs may include a replicon RNA including RNA which encodes the alphavirus packaging sequence, the inserted heterologous RNA, and the alphavirus capsid protein, but both the alphavirus E1 glycoprotein and alphavirus E2 glycoprotein are deleted therefrom; and a first helper RNA includes RNA encoding both the alphavirus E1 glycoprotein and the alphavirus E2 glycoprotein.
In another embodiment, the set of RNAs also includes a second helper RNA separate from the replicon RNA and the first helper RNA. In this embodiment, the second helper RNA encodes, in trans, at least one structural protein, which is different from the structural protein encoded by the replicon RNA and by the first helper RNA. Thus, for example, the set of RNAs may include a replicon RNA including RNA which encodes the alphavirus packaging sequence, and the inserted heterologous RNA: a first helper RNA including RNA which encodes a promoter sequence and an RNA encoding both the alphavirus E1 glycoprotein and the alphavirus E2 glycoprotein; and a second helper RNA including a promoter sequence and RNA which encodes the alphavirus capsid protein, with the replicon RNA, the first helper RNA, and the second helper RNA being in trans from each other, on separate molecules.
As a fourth aspect, the present invention provides infectious VEE replicon particles containing RNA encoding a promoter sequence, and an inserted heterologous RNA, and wherein RNA encoding at least one alphavirus structural protein is deleted from the RNA so that the infectious virus particle is replication defective.
As a fifth aspect, the present invention provides a pharmaceutical formulation comprising infectious alphavirus particles as described above, in an effective immunogenic amount in a pharmaceutically acceptable carrier.
The foregoing and other aspects of the present invention are explained in detail in the detailed description set forth below.